JPH01158834A - Cancelling circuit and transmission system - Google Patents

Abstract

PURPOSE:To improve the line utilizing efficiency by constituting a bridge circuit able to reach the balance state in full or part of band in a frequency band to be sent in a wired transmission line so as to attain 2-way simultaneous communication. CONSTITUTION:The bridge circuit comprising the combination of a transformer and an operational amplifier is provided with a frequency characteristic correction and phase circuit. Thus, the circuit is corrected for the effect of the impedance change in the transmission line and the unbalance state caused due to a component itself of the circuit to obtain a relative balance state and the remarkable improving effect of a crosstalk characteristic is obtained. Since the 2-way communication is attained simultaneously by using a carrier of the same frequency, the frequency band not required in use is used for other transmission of a voice signal or a data to attain efficient communication.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cancellation circuit in communications such as video telephones and modems that perform wired and wireless communications, and a transmission system using this circuit.

(Prior Art) Conventionally, terminal devices such as telephones and modems have used a method of simultaneously communicating in both directions using only the - line, but in order to do this, they have to communicate in both directions using the signals they themselves send out. , it is necessary to separate the signals sent from the other party, and it is well known that if this separation ability (crosstalk characteristics) is low, it will lead to howling in telephones and an increase in errors in modems, etc. .

Conventional telephones and modems use something called a lick hybrid circuit (hereinafter referred to as "rHYB circuit") that separates the transmitted signal and received signal. The Talostork characteristics of
(4-1) in Figure 4 (4-1), the performance is considered to be sufficient for a telephone intended for telephone calls. It was impossible to perform two-way simultaneous communication using the same carrier frequency using a modem or the like. In this slanted modem, etc., the necessary separation ability was obtained by using a frequency division method, etc., which separates the transmitting frequency and the receiving frequency, in combination with the HYB circuit.

(Problem to be solved by the invention) However, when considering line usage efficiency, if bidirectional communication can be performed simultaneously using carrier waves of the same frequency,
This makes it possible to use frequency bands that are no longer needed for transmitting other audio signals or data, allowing for more efficient communication.

(Means for Solving the Problems) A feature of the present invention is that simultaneous two-way communication is possible by configuring a bridge circuit that can be in a balanced state over the entire or part of the transmittable frequency band on a wired transmission line. It is possible.

Another feature of the present invention is that all! The above canceling circuit is provided on both the J and L sides to enable simultaneous bidirectional communication even at the same frequency.

(Example) For a better understanding of the present invention, a conventional HYB circuit will be included in the description. The circuit shown in FIG. 1 is a HYB circuit constructed by combining a transformer and an operational amplifier, which are often used these days. This HYB circuit constitutes a bridge circuit, and the condition for this bridge circuit to be balanced is when the telephone line is a pure resistance component of 600Ω, and the transformer T is an ideal transformer and C=0, it is in a balanced state, and the input from Vi The detected signal is not output to vO. However, the impedance characteristics of an actual telephone line are not pure resistance components, and the performance of the transformer is far from an ideal transformer, so the crosstalk characteristics actually obtained are as shown in Figure 4 above.
4-1). As you can see from this figure, about 1/3 of the signal Vi that you sent out <-10d
It is obvious that it is difficult to simultaneously transmit and receive signals on the same frequency using this circuit, in which B) is output from 0 and received as a received signal.

Therefore, the method according to the present invention was invented to improve this crosstalk characteristic.

When considering the reason why the conventional HYB circuit does not become balanced, it may not be the telephone line or the 600Ω pure resistance component, but the elements used in the YB circuit itself (transformer, capacitor C) have a large influence. This generally consists of a tuned circuit consisting of a transformer and a capacitor C to provide a bandpass effect in order to eliminate line noise, etc., but in this case, at frequencies other than the resonant frequency, A phase difference occurs between the voltages at point A and point B, resulting in an unbalanced state.

Therefore, in the present invention, by adopting the configuration shown in FIG. 2, the voltage and phase difference between points A and B are made relatively zero, and the bridge circuit thus configured is brought into a balanced state. As a result, a significant improvement in losstalk characteristics was obtained.

FIG. 3 shows a more specific circuit example.

In this circuit example, the purpose is to improve crosstalk characteristics around 2 KHz to 3 KHz, and the characteristics obtained thereby are shown in FIG. 4 (4-2).

To explain the circuit of FIG. 3, a bridge circuit is formed by a transformer T1, a capacitor C1, a resistor Ra, a transformer T2 connected to a resistor of about 600Ω as a load, a capacitor c2, and a resistor Rb connected to the line side. Transformers T1 and T2 are of the same standard, and CI =
If C2, Ra=Rb, the amplitude and phase changes caused by these elements are relative, and Va2 and v
b are almost the same, but since a telephone line is connected to the transformer T1 and a pure resistor is connected to the transformer T2, an error occurs due to a substantial change in the impedance of the telephone line.

Same as telephone line as load of transformer T2 = 6-
A bridge circuit can be configured using an element that changes the impedance as a load, but in the present invention, the difference is made relatively zero by correcting this using a high frequency amplitude correction circuit and a phase shift circuit. This is an equivalent bridge circuit. Vb2 and Va3 are V when VL is input
b2 = Va3, and it is not output to ■0, but is sent to the telephone line. Furthermore, since the signal sent through the telephone line appears on Vb2 but not on Va3, it is possible to separate the signal VL sent by itself from the signal received.

This circuit example is designed for use in videophones, etc.
Among the frequency bands that can be transmitted by telephone lines, 2KHz to 3.
It is possible to perform two-way simultaneous transmission of image signals at 4KHz using the same carrier wave frequency or adjacent carrier wave frequencies, and to simultaneously perform two-way communication of audio signals for telephone calls within a band of 300Hz to 2KHz. It is something to do. Figure 3 shows a circuit that is designed to be used as described above; it does not correct the frequency band used for audio signals, but it also shows a circuit that corrects the frequency band for image signal transmission, which is greatly affected by crosstalk. 2KH because it is a characteristic
The characteristics below z have deteriorated, but by increasing the number of amplitude and phase correction circuits or the elements for correction as shown in Figure 5, good characteristics can be achieved over a wider band. can get. This makes it possible to apply this to full-duplex data communications using the same carrier frequency using high-speed modems, etc. In this case, since phase characteristics are also important depending on the modulation method, good results can be obtained by passing the received signal VO through a circuit having a phase characteristic opposite to that of the phase circuit in the circuit example.

Note that the element constants for amplitude and phase correction in the circuit may be fixed, semi-fixed, or automatically adjusted (autobalance) depending on the performance required; however, in the case of automatic adjustment, Vb2 and Va3 It is sufficient to detect the amplitude and phase of and perform control so that they match.

Several embodiments of transmission methods made possible by using the circuit according to the invention will now be described.

FIG. 6 is an example of simultaneous two-way communication of image data using one telephone line. Traditional method, half 2
Compared to the multiplex system, transmission time can be shortened because transmission and reception can be performed simultaneously in both directions. In the case of half-duplex, in order to perform simultaneous two-way communication, the transmission speed is lowered and multiplexing is performed using a frequency division method. Alternatively, it was necessary to use two telephone lines, one for sending only and one for receiving, but if the same carrier wave is used for sending and receiving with the configuration shown in Figure 6, the transmission speed will not decrease and the telephone line can be used as one line. Since it only requires the following steps, it is possible to construct a low-cost system.

Naturally, if the telephone line shown by the chain line in FIG. 6 is also used, this audio configuration becomes a videophone system.

In this example, the configuration is for image communication, but it can also be used for data communication using other modems or the like.

FIG. 7 is an example of a case where higher speed transmission than that in FIG. 6 is required. In this figure, two lines are used in parallel, but if higher speed is required, the same thing can be done using a larger number of lines. This example is also shown as an image data transmission system, but when transmitting image data captured by such a camera, there is a limit to the frequency range that can be transmitted over a telephone line.
It is necessary to store image data once input from a camera in a storage circuit such as a memory, and then read it out and transmit it at a signal speed that can be transmitted over a telephone line. At this time, if two or more lines are used in parallel at the same time, even if this reading speed is doubled, if two lines are used, the speed will be the same as when using one line for each line. The faster the signal can be sent, the faster the signal can be sent.

On the receiving side, the signals sent through multiple lines are demodulated, the data is combined, stored in memory, and displayed by reading it out at a speed suitable for the image display section. In this example as well, if the telephone line shown by the dashed line in the figure is used in conjunction with the telephone line in the same way as in FIG. 6, a video telephone system is created.

FIG. 8 shows an example of a transmission system in which audio signals for telephone calls are multiplexed by a frequency division method as an application example of FIG. 7. When considering the communication of image data, etc., it is well known that in order to increase the transmission speed, it is advantageous to have the carrier frequency close to the upper limit of the frequency range that can pass through the transmission line. Moreover, it is also possible to narrow the occupied band by using the SSB method or the like. For example, 2KT(z~3.'
Considering that 4KH2 is used as a signal band for image data, using the Talostalk cancellation circuit according to the present invention enables simultaneous transmission and reception using the same carrier frequency. It is conceivable to send and receive data.

In FIG. 8, this band is used for transmitting audio signals for making phone calls. In this example, audio signals are not multiplexed on line 1, and only line 2 is multiplexed.
Applications such as multiplexing both lines and stereophonizing the audio signal may also be considered.

The same thing is possible when a system using two or more lines is configured, and in the case of a video conference, etc., it is considered that multi-channeling of audio signals is also necessary. In the case of Fig. 8, since the audio signal and the image data are multiplexed and transmitted, there is no need to use a separate telephone line for telephone calls as in Figs. 6 and 7, so it is possible to reduce costs. However, since multiplexing is performed using a frequency division method, there is a drawback that the clarity of the audio signal decreases.

Therefore, the method shown in FIG. 9 is a method for solving this problem. FIG. 9 shows an example where two or more lines are used to speed up the transmission time. In a configuration using two or more lines, if each line has an unused frequency band, it can be applied by using that portion.

For image data signals, if the frequency band for image data transmission is divided, for example, from 2 KHz to 3.4 KHz using the same method as shown in FIG. 8, in the example shown in FIG.
The band from 300 Hz to 2 KHz for each of the two lines 2 is an unused band. Audio signals for calls are multiplexed into this part, but the usable frequency range is 300.
Since the frequency range is Hz to 2 KHz, it is not possible to send voice signals in the 300 Hz to 3.4 KHz frequency band that is used when making telephone calls with ordinary telephones.

Therefore, the frequency range of 300Hz to 3.4KHz, which is said to provide sufficient clarity for a telephone conversation, is divided into frequencies using a filter and divided into a high frequency side and a low frequency side. In the example in Figure 9,
Since two lines are used, the line is divided into two, but the number of lines to be divided is arbitrary depending on the number of lines used or the width of the unused frequency band of each line. 2
When dividing, if the frequency at the dividing point is IKHz, the lower side is a frequency component of 300Hz to IKHz, and the higher side is IKH.
The signal has frequency components of z to 3.4 KHz. This is transmitted as is through line 2 on the low frequency side. Since the high frequency side is a frequency component of IKHz to 3.4KHz, if it is sent to line 1 as it is, it will overlap with the image data signal, so it is impossible to transmit it as it is. This high frequency side signal is 1/1/1 by a frequency shift down circuit.
Set it to 2. As a result, a frequency signal of IKHz to 3.4KHz is converted to a signal of 500Hz to 1.7KHz, so that if transmitted through line 1, it can be multiplexed with an image data signal.

On the receiving side, the low range 300 Hz to IKHz of the audio frequency sent through line 2 is extracted by a filter, and the high range 50 Hz of the audio frequency sent through line 1 is extracted.
Simultaneous two-way communication of 300 Hz to 3.4 KHz signals and image data is possible by doubling the frequency to IKHz to 3°4 KH2 and outputting it to the 0 Hz to 1.7 KHz shift up circuit. Naturally, the frequency of the frequency division point is not limited to IKHz,
1/2 frequency shift up and down shift
．． This value is not limited to twice, as it is considered suitable for configuring an actual circuit, and can be determined based on the number of lines to be used and unused frequency bands when configuring an actual system. .

In order to increase the efficiency of transmission path usage, it is possible to: ■ Increase the transmission rate; ■ Create a configuration that allows full duplex communication rather than half duplex communication, but when considering a videophone system, it is possible to Because there is a need to transmit audio signals for
It is conceivable to multiplex this audio signal using a frequency division method or the like and transmit it together with the image data. At this time, in an actual telephone conversation, it is highly unlikely that voice signals will be sent and received continuously without any gaps.
By detecting this period of silence and using the band used for transmitting audio signals during a call to transmit image data, it is possible to further improve the efficiency of use of the transmission path. becomes.

FIG. 10 is a block diagram when performing this method. In this example, by providing a Talostalk cancellation circuit, it is possible to perform two-way simultaneous transmission and reception, but this method itself is a method that multiplexes data such as audio signals and images for the purpose of communication. It can be applied to all types of communication, and can be performed in the same way when using two or more lines other than when using one line, regardless of whether it is wired or wireless.

To explain the example shown in Figure 10, considering that it is to be used as a videophone, image data and voice signals for calls are multiplexed using a frequency division method, and simultaneous two-way communication of image and voice is achieved using one line. It made it possible. When a user is talking, the operation is exactly the same as that of a normal frequency division multiplexing method, but each terminal constantly detects whether or not the user is speaking, and It also sends out some kind of signal or data that can convey the status to the terminal on the side. For example, to give an example of this signal, if a telephone line is used as the transmission path,
Its passable frequency band is 300Hz to 3.4KHz
It is. In order to multiplex this image and audio signal, 40
0Hz to 1.5KHz is audio (for calls), 2K
When the image signal band ranges from Hz to 3 KHz (Fig. 11), ■ put it in 1.75 KHz between these two signal bands ■ 300 Hz, which is the lower limit of the transmittable frequency, and the band used for audio. 350Hz, which is between the lower limit of 400Hz ■3KHz, which is the upper limit of passable frequency
3, which is the upper limit of the frequency used as an image signal between
This is possible by using 3 or 2 KHz, etc. between the two KHz as a signal (or data) to convey the status of the caller to each other's terminals.

This signal allows each terminal to recognize when there is no audio input, so at this point both terminals can be used for calls until then by turning on switches S1 and 82 in the figure. Image data can be transmitted even in the previously used band. Naturally, the frequency and occupied band of the carrier wave used at this time are 400Hz to 1.5Hz.
Since it needs to be within 5KH2, the transmission rate is also lower than that of the image data signal which uses 2KHz to 3KHz. In the case of a videophone, the image data to be sent is temporarily stored in memory, and can be accessed randomly both in writing and reading, so by using the CPU to perform this control, other detection and , the operation can be controlled based on the state of this detection signal. As for the operating speed of the CPU, if the data speed is the same as that for transmission over a telephone line, it is sufficient to process data with approximately 8 bits.

While both users are not talking, transmission is performed using both the image data signal band and the audio signal band. As mentioned above, memory access can be done randomly. For example, if the image data in memory is from address 0 to address 100, the data from address 0 in the image signal band will be accessed in the audio signal band. In this case, transmission may be performed in reverse from address 100.

When this operation is being performed, when either user starts talking, each terminal can recognize this based on the previous recognition signal or data.

At this time, each terminal returns to its normal operating state. At this time, the voice input signal is delayed using a BBD circuit or the like, as shown in the figure, because the voice signal cannot be made available unless the operation is switched first. As a result, the voice uttered by the caller can be transmitted to the other party, but as long as the delay time is set to about 100 ns or less, it is considered that there will be no problem at all in use. The muting circuit in the audio output section prevents this signal sound from being output since image data is sent even in the audio signal band. In this example, image data is distributed and transmitted when the frequency band for audio signals is not used, but conversely, when there is little image data that needs to be transmitted, for example in a videophone system, the image data is transmitted in succession. When transmitting image data, if you compare each screen of images taken with a camera and there are many parts that do not change, or in other words, do not move, it is better to send only the difference data from the previous image. become. When using such a method,
The amount of image data that needs to be transmitted is reduced, and there is no problem in practical use even when communication is performed at a low transmission rate. To send image data over a telephone line, modulation is performed, but by lowering the rate of this modulation, the occupied frequency band becomes narrower. This makes it possible to increase the frequency that limits the high range for audio signals.

At this time, it is possible to transmit up to the high frequency range of the voice signal, thereby achieving the effect of improving the clarity of the call. Furthermore, if the above two methods are used in combination, the efficiency of line usage is greatly improved, and a system with high sound quality and high speed can be constructed depending on the usage conditions. Of course, switching based on this state can also be done manually, by detecting the call status by detecting the audio signal, transmitting by comparing data in memory, etc., or by detecting the amount of image data required.
The determination can also be made automatically using the CPU.

In addition to the method of performing the switching operation by detecting the status of both sides as in this example, there are other methods that can be considered, such as a method of performing switching based on the usage status of one side and determining the operation status of the other side. It will be done.

In addition, in FIG. 10, the changeover section switch S1.32 is for explanation, and actually changes the electrical operation by the CPU or the like.

The example shown in FIG. 6 and 10 can be used regardless of whether it is wired or wireless.

(Effects of the Invention) As explained above, according to the present invention, the performance of the transmission line used for communication can be used with high efficiency, it can be configured at low cost, and it can be used to connect various terminals to general households, etc. It can promote the spread of equipment.

[Brief explanation of the drawing]

Fig. 1 is a conventional HYB circuit diagram, Fig. 2 is a block diagram showing the basic configuration of the present invention, Fig. 3 is a diagram showing a specific example of the circuit of the present invention, and Fig. 4 (4-1) is a conventional HYB circuit diagram. FIG. 4 (4-2) is a diagram showing the HYBY2O2 losstalk characteristic of the present invention. FIG. 5 (5-1) to (5-3> are diagrams each showing an example of a frequency characteristic correction circuit. Figure 5 (5-4> is a diagram showing an example of a phase correction circuit;
5-5> is a diagram showing an example of a circuit when frequency characteristic correction and phase correction are performed in one circuit, FIGS. 6 to 10 are block diagrams showing each embodiment of the transmission method, and FIG. 10 is a diagram illustrating an example spectrum of a method for multiplex transmission of recognition signals when using the transmission method according to the example shown in FIG. Patent applicant for the above: Mucom Co., Ltd. Figure 1 Figure 2 Figure 3 Cause (V mouth 2 - VO2) (5'') C) Coco

Claims (1)

[Claims] 1. A cancellation circuit that enables two-way simultaneous communication by configuring a bridge circuit that can be in a balanced state over the entire or part of the transmittable frequency band on a wired transmission line. 2. In claim 1, the bridge circuit is:
A cancellation device that is equipped with a frequency characteristic correction and a phase circuit, and corrects both the influence of impedance changes in the transmission path and the unbalanced state caused by the elements themselves, and obtains a relative balanced state. circuit. 3. A cancellation circuit is provided on both the R side and the L side across the transmission path, and the cancellation circuit constitutes a bridge circuit that can be in a balanced state over the entire transmittable frequency band or within a part of the frequency band. A transmission method that is characterized by enabling simultaneous two-way communication even on the same frequency.